Event related potentials recorded in Dorsal Simultanagnosia

Area of Science:

• Neuroscience
• Clinical Neurophysiology
• Visual Neuroscience

Background:

• Dorsal Simultanagnosia is a visual processing disorder resulting from bilateral parieto-occipital lesions.
• Understanding the impact of such lesions on neurophysiological measures like VEPs and ERPs is crucial for diagnosis and understanding brain function.

Observation:

• VEPs were recorded in response to patterned stimuli at varying spatial frequencies (1, 2, 4 cpd) in a patient with dorsal Simultanagnosia.
• Event-related potentials (ERPs) were assessed using visual and acoustic odd-ball paradigms.
• VEPs showed normal N1-P1-N2 components with preserved spatial frequency sensitivity and unaffected latency/amplitude regardless of stimulus visibility.

Findings:

• Despite severe bilateral parieto-occipital lesions causing Simultanagnosia, VEPs remained intact, exhibiting normal components and spatial frequency sensitivity.
• Visual ERPs revealed an early NA-effect and N2-P3 components, with P3 abnormalities showing similar topography for both visual and acoustic odd-ball tasks.
• P3 amplitude was reduced when visual stimuli were missed, indicating a link between attentional processing and stimulus detection.

Implications:

• Severe bilateral parieto-occipital lesions causing Simultanagnosia do not abolish fundamental visual evoked potentials (VEPs) or event-related potentials (ERPs).
• The findings suggest that core visual processing pathways, detectable by VEPs, may remain functional even when higher-level visual awareness is compromised.
• Abnormalities in P3 topography across different sensory modalities highlight the widespread impact of these lesions on attentional networks.